A V-twin is a two cylinder internal combustion engine where the cylinders are arranged in a V configuration.
This arrangement is common on motorcycles, the engine can be mounted in transversal position like on Harley-Davidsons, Ducatis and many recent Japanese motorcycles. The longitudinal V-twin as seen on Moto-Guzzis and some Hondas is less common. This position is well adapted to transmission shafting, but has the disadvantage of causing a torque reaction that tend to lean the motorcycle on the side.
The most obvious configuration for a V-twin is a 90° angle, but others angle can be seen like the 45° Harley-Davidson, the 75° Suzuki and the 60° Aprilia.
A 90° V-twin can achieve perfect primary balance but has some secondary imbalance.
The longitudinal V-twin should be viewed as an alternative to the flat-twin configuration. The flat-twin is perfectly balanced but larger that the V-twin. This require the flat-twin to be mounted high on the motorcycle to avoid cylinders head touching the ground in curve. On the other hand the V-twin could be mounted lower and could result in a lower center of gravity for the whole motorcycle.
